Autoinjector

ABSTRACT

An autoinjector comprising a body ( 1, 2 ), and a reservoir (S) containing fluid and including a piston (P) and a needle (A), such as a pre-filled syringe, said autoinjector further comprising a piston rod ( 5 ) that is suitable for co-operating with the piston (P) of said reservoir (S), said piston rod ( 5 ) being movable between a rest position and an injection position in which said piston rod ( 5 ) has moved the piston (P) of the reservoir (S) so as to inject the fluid through the needle (A), an actuator spring ( 6 ) being provided so as to urge said piston rod ( 5 ) towards its injection position, the autoinjector further comprising a force-adjustment system ( 7, 8 ) that exerts a force (F 2 ) on said piston rod ( 5 ), said force (F 2 ) adding to the force exerted by said actuator spring ( 6 ) on said piston rod ( 5 ) at the beginning of injection, so as to amplify the force exerted on said piston (P) by said piston rod ( 5 ) at the beginning of injection.

BACKGROUND OF THE INVENTION

The present invention relates to an autoinjector.

Autoinjectors are well known in the prior art. The purpose of suchdevices is mainly to inject the contents of a syringe automatically intothe body of a patient. Various systems exist for making the penetrationof the needle into the body of the patient and the injection of thefluid contained in the syringe automatic. Autoinjectors are relativelycomplex devices that must satisfy a certain number of constraintrequirements in order to be reliable. The robustness of the device, itshandling, and its ease of use for the user are also important elements.In addition, since most autoinjectors are for single use, the cost ofmanufacture and of assembly is also a factor that needs to be taken intoaccount.

Numerous autoinjectors exist on the market, but they all present acertain number of drawbacks.

Thus, for autoinjectors that use the same spring both for initialpricking then for injection proper, the spring must be sufficientlystrong to guarantee the injection stage in full. This is particularlytrue given that a relatively large force is generally required at thebeginning of the injection stage, in order to start the movement of thepiston of the syringe. As a result, the spring delivers its maximumpower during pricking, which may make the pricking stage painful.Furthermore, with such a spring that is very powerful during pricking,there exists a significant risk of breaking the collar of the syringe,in particular when it is a glass syringe.

Documents WO 2009/010591 and US 2001/005781 describe prior-art devices.

An object of the present invention is to provide an autoinjector thatdoes not have the above-mentioned drawbacks, and that makes it possibleto satisfy the various major requirements and constraints for safe andreliable use of the autoinjector.

Another object of the present invention is to provide an autoinjectorthat is reliable and safe in use, that makes it possible to guaranteethat all of the fluid is dispensed to the desired location, and that issimple and inexpensive to manufacture and to assemble.

The present invention thus provides an autoinjector comprising a bodyand a reservoir containing fluid and including a piston and a needle,such as a pre-filled syringe, said autoinjector further comprising apiston rod that is suitable for co-operating with the piston of saidreservoir, said piston rod being movable between a rest position and aninjection position in which said piston rod has moved the piston of thereservoir so as to inject the fluid through the needle, an actuatorspring being provided so as to urge said piston rod towards itsinjection position, the autoinjector further comprising aforce-adjustment system that exerts a force on said piston rod, saidforce adding to the force exerted by said actuator spring on said pistonrod at the beginning of injection, so as to amplify the force exerted onsaid piston by said piston rod at the beginning of injection.

Advantageously, said force-adjustment system comprises two pivot membersthat co-operate with said piston rod, said pivot members being connectedtogether by two resilient elements.

Advantageously, said pivot members pivot about pivot pins that areparallel and stationary relative to said body.

Advantageously, said resilient elements are fastened to said pivotmembers via parallel movable pins, such as rods having two side edges,that are formed on said pivot members.

Advantageously, when the piston rod moves towards its injectionposition, said movable pins are arranged behind said stationary pins inthe travel direction of said piston rod, said loaded resilient elements,at the beginning of travel of the piston rod towards its injectionposition, causing said pivot members to pivot in such a manner as torelax said resilient elements, thereby creating an amplification forceat the beginning of injection.

Advantageously, each pivot member includes a plurality of projectionsthat are suitable for co-operating with a plurality of radialprojections of the piston rod.

Advantageously, said autoinjector is triggered by an axial button, oneor more side buttons, or a slidable sleeve.

Advantageously, prior to injection, said piston rod is initially movedby said actuator spring between said rest position and a prickingposition in which said piston rod has moved said reservoir relative tosaid body so as to perform pricking.

Advantageously, during pricking, the piston rod co-operates with thepiston of the reservoir so as to move said reservoir relative to thebody.

In a variant, during pricking, the piston rod includes a resilientmember, such as an O-ring arranged in a groove of the piston rod, thatco-operates with a collar of the reservoir so as to move said reservoirrelative to the body.

BRIEF DESCRIPTION OF THE DRAWINGS

These characteristics and advantages, and others, of the presentinvention appear more clearly from the following detailed description,given by way of non-limiting example, and with reference to theaccompanying drawings, in which:

FIG. 1 is an exploded diagrammatic perspective view of the components ofan autoinjector, in an advantageous first embodiment;

FIG. 2, FIG. 3, FIG. 4, FIG. 5, FIG. 6, FIG. 7, FIG. 8, FIG. 9, FIG. 10and FIG. 11 are diagrammatic section views showing the successivesequences of the present invention, in the FIG. 1 embodiment;

FIG. 12 and FIG. 13 are simplified diagrammatic views of the operationof the present invention, respectively in the damping stage at the endof pricking and in the amplification stage at the beginning ofinjection;

FIG. 14, FIG. 15 and FIG. 16 are diagrammatic section views of threeactuator variants in the present invention;

FIG. 17 is an exploded diagrammatic perspective view of the componentsof an autoinjector, in an advantageous second embodiment;

FIG. 18 is a section view of a detail of the FIG. 17 device;

FIG. 19 is a side view of a detail of a portion of the FIG. 17 device;

FIG. 20 is a view similar to the view in FIG. 19, as seen from below;

FIG. 21, FIG. 22, FIG. 23, FIG. 24 and FIG. 25 are diagrammatic sectionviews showing the successive sequences of the present invention, in theFIG. 17 embodiment;

FIG. 26, FIG. 27, FIG. 28, FIG. 29 and FIG. 30 are diagrammatic sideviews showing the successive sequences of FIGS. 21 to 25; and

FIG. 31, FIG. 32, FIG. 33 and FIG. 34 are section views showing anotherembodiment of the invention.

The autoinjector is described below with reference to a plurality ofadvantageous embodiments. It should nevertheless be observed thatautoinjectors, which are complex appliances, comprise a plurality ofmodules for performing a plurality of functions. The various modules maybe used separately and independently of one another, without necessarilybeing combined with the other modules, and in particular they could beused in autoinjectors of shape that is different from the shape shown inthe drawings. Furthermore, it should be observed that the drawings arediagrammatic views, which do not necessarily represent the exact shapeof the components of an autoinjector, and they are not necessarily toscale, in particular for purposes of clarity. In addition, the drawingsdo not necessarily represent all of the component elements of anautoinjector, but only the elements necessary for operation of thepresent invention. Thus, various additional and/or complementaryelements and modules could be associated with the autoinjector shown inthe figures.

With reference to FIG. 1, the various components of the autoinjector, inan advantageous first embodiment, are shown in an exploded view.

In the order of the numerical references, the autoinjector comprises alower body 1, an upper body 2 containing a sleeve 3, an axial actuatorbutton 4, a piston rod 5, an actuator spring 6, and two pivot members 7that are interconnected by means of two resilient elements 8, which inthis embodiment are in the form of springs. The resilient elements 8 canbe seen in FIGS. 1, 12, and 13, but not in FIGS. 2 to 11 and 14 to 16for purposes of clarity.

It should be observed that the lower and upper bodies could be replacedby a single body.

A reservoir S may be inserted into said autoinjector, in particular intoits lower body 1. The reservoir S contains fluid and includes a piston Pand a needle A. The piston P is adapted to move in said reservoir S soas to inject the fluid through said needle A.

The present description is made with reference to a syringe S that maybe of any type. More generally, it is understood that the term “syringe”in the present description encompasses any type of reservoir associatedwith a needle. Preferably, the reservoir S is a pre-filled syringe.

The lower body 1, at its leading end (in the travel direction of thesyringe S), includes an opening through which the needle A passes duringthe pricking stage.

The lower body 1 may include resilient tabs 15, or any other holdingmeans, that are suitable for holding the syringe S in its rest positionin which the needle A does not project out from said lower body. Duringactuation, the resilient tabs 15 release the syringe S that can thenmove axially relative to the lower body 1 so as to enable the needle toproject therefrom and perform pricking.

The upper body 2 is fastened to the lower body and it may include acentral sleeve 3 that is suitable for housing the piston rod 5 and thespring 6.

The axial actuator button 4 may be mounted to slide axially relative tothe upper body 2, and in contact with the piston rod 5. Thus, bypressing on the axial button 4 so as to drive it axially into the upperbody 2, the piston rod 5 is moved axially, thereby making it possible totrigger the device as described below.

The piston rod 5 includes a trailing end 54 and a leading end 55 in thetravel direction of the piston rod 5 in the upper body 2.

In this embodiment, the trailing end 54 co-operates with the axialactuator button 4.

The purpose of the leading end 55 is to contact the piston P of thesyringe S, so as to move said piston P and thus inject the fluidcontained in the syringe S through the needle A.

The piston rod 5 also includes a plurality of radial projections 52, 53:a first radial projection 52, that is close to the leading end 55, andthat defines a shoulder-forming leading surface 51; and a second radialprojection 53, that is axially offset from said first radial projection52 towards the trailing end 54, and that defines both a leading surfaceand a trailing surface. Naturally, this is only an embodiment example,and a person skilled in the art is capable of making the radialprojections and shoulders in a way that is different from the way shownin the drawings. In particular, said radial projections 52, 53 are notnecessarily in the leading portion of the piston rod 5, as shown in thedrawings, but they could be made on another portion of the piston rod 5,e.g. to the rear of said piston rod, in particular behind the bearingpoint of the actuator spring 6 that is at the rear in the traveldirection of the piston rod during actuation.

The actuator spring 6 bears firstly against the sleeve 3 of the upperbody 2, and secondly against the piston rod, e.g. against a fourthshoulder 58 that is axially offset from said third shoulder 53 towardsthe trailing end 54.

The pivot members 7 are advantageously assembled in pivotable manner onthe upper body 2, and they are advantageously identical. They arearranged on either side of the piston rod 5. They are not movableaxially relative to said lower body 1, but only in pivoting about theirpivot pins 79, which are parallel. In a variant, they could be assembledin some other way, in particular on the lower body 1.

Each pivot member 7 includes a plurality of projections 71, 72, 73: afirst projection 71 that is suitable for co-operating with the leadingsurface 51 of the first radial projection 52 of the piston rod 5; asecond projection 72 that is suitable for co-operating with the leadingsurface of the second radial projection 53; and a third projection 73that is suitable for co-operating with the trailing surface of thesecond radial projection 53. Naturally, other embodiments can also beenvisaged.

The resilient elements 8 connect the two pivot members 7 together. Theprinciple consists in combining two stationary pivot pins, namely thepivot pins 79 of the two pivot members 7, with two movable pins, namelythe fastener points 78 of the pivot members 7 on which the resilientelements 8 are fastened.

Thus, as can be seen in FIG. 1, the first resilient element 8 isfastened firstly to a first fastener point of the first pivot member,and secondly to a first fastener point of the second pivot member, andthe arrangement is similar and symmetrical for the other resilientelement. Preferably, each pivot member 7 includes a rod 78 having twoprojecting side edges. The first resilient element thus connects thefirst projecting edges together, and the second resilient elementconnects the second projecting edges together. Advantageously, when theresilient elements 8 are springs, they are identical and include eyelets88 that are suitable for fastening to said first and second projectingedges 78 of the pivot members 7. In a variant, the resilient elementscould be different, e.g. in the form of O-rings or of other elementsmade of elastically-deformable material. The use of rings made ofelastic material, such as O-rings, to replace the springs shown in thedrawings make it possible, in particular, to reduce the amount of spacethe system occupies radially.

The present invention provides a force-adjustment system that issuitable for exerting a force F2 on said piston rod 5. At the beginningof injection, the force F2 is added to the force exerted by the actuatorspring 6 on the piston rod 5, so as to amplify the force that is exertedon said piston P by said piston rod 5 at the beginning of injection.Advantageously, it is also possible, at the end of pricking, to providea force F1 that opposes the force exerted by the actuator spring 6 onthe piston rod 5, so as to decrease the force exerted on said reservoirS by said piston rod 5 at the end of pricking.

Thus, when the movable pins 78 are axially offset relative to thestationary pivot pins 79, they exert a force by means of the resilientelements 8. When said movable pins 78 are arranged in front of saidstationary pins 79 in the travel direction of the piston rod 5, theforce opposes the pivoting imparted to said pivot members 7 by saidpiston rod 5. The pivoting of the pivot members 7 is thus braked by saidresilient elements 8. In contrast, when said movable pins 78 arearranged behind said stationary pins 79 in the travel direction of thepiston rod 5, the force acts in the same direction as the pivotingimparted to said pivot members 7 by said piston rod 5. The pivoting ofthe pivot members 7 is thus amplified by said resilient elements 8. Whenthe stationary and movable pins 79, 78 are in alignment, there is aneutral point in which said resilient elements 8 do not influence thepivoting of the pivot members 7. It is in this position that the systemtoggles from a “braking” or “damping” state into an “amplification”state.

FIGS. 2 to 11 show the actuation sequences of the FIG. 1 autoinjector.

In FIG. 2, the autoinjector is in the rest position prior to actuation.In this rest position, the needle A of the syringe S is arranged insidethe lower body 1. Said movable pins 78 are arranged in front of saidstationary pins 79 in the travel direction of the piston rod 5, as showndiagrammatically in FIG. 12. The actuator spring 6 urges the piston rod5 towards the piston P of the syringe S, but the piston rod 5 is held inthe rest position by the first projection 71 of the pivot members 7 thatco-operates with the first shoulder 51 of the piston rod 5. Under thepressure of the actuator spring 6, said first shoulder 51 of the pistonrod 5 pushes the first projection 71 of the pivot members 7 in pivoting,but such pivoting is opposed by the resilient elements 8, delivering aforce that is selected in appropriate manner so as to provide a restposition that is stable. The resilient elements 8 thus counterbalancethe force of the actuator spring 6, and without outside intervention,the device is blocked in its rest position.

When the user wishes to use the autoinjector, the user takes hold of thedevice, e.g. at the upper body 2, and presses on the axial actuatorbutton 4. In this way, the user moves the piston rod 5 axially, therebycausing the pivot members 7 to pivot.

Trigger variants are shown in FIGS. 14 to 16. FIG. 14 shows triggeringby an axial button 4 as described above, and requires the application ofan axial trigger force in the direction of arrow 1. FIG. 15 shows avariant in which the trigger force is applied sideways in the directionof arrow(s) 2, by one or two side buttons 40. FIG. 16 shows anothervariant in which the trigger force is applied axially in the directionof arrow 3, by a slidable sleeve 400 that is arranged around the lowerbody 1, in contact with the injection site.

The pivoting of the pivot members 7 generated by the actuation forcecauses the first projection 71 and the first shoulder 51 to disengagefrom each other. This thus releases the piston rod 5 that is then movedaxially under the effect of the actuator spring 6. This causes thesyringe S to move in the lower body 1 and thus causing pricking, asshown in FIGS. 3 and 4.

The syringe S may be moved by contact between the leading end 55 of thepiston rod and the piston P of the syringe S. In a variant, as shown inparticular in FIGS. 3, 4, and 13, a resilient member 9, such as anO-ring, may be mounted on the piston rod 5, e.g. in an appropriategroove, the resilient member 9 co-operating with the collar C of thesyringe S during the pricking stage, and then disengaging from saidpiston rod 5 during the injection stage. This implementation avoids anycontact between the piston rod and the piston during pricking.

During the pricking stage, the first projections 71 and/or the secondprojections 72 of the pivot members 7 slide along the piston rod 5between said first and second radial projections 52, 53. In theembodiment shown, the first projections 71 slide along the piston rod 5between said first and second radial projections 52, 53, while theprojections 72 do not encounter any obstacles since they are situated inappropriate recesses of the piston rod 5. The pivot members 7 maypossibly continue to pivot a little while sliding, e.g. via slopingramps formed on the piston rod 5 between the first radial projection 52and the second radial projection 53. This makes it possible to provide alittle damping or braking during pricking.

When the second projection 72 of the pivot members reaches the leadingsurface of the second radial projection 53 of the piston rod 5, thepricking stage is not completely terminated. This can be seen in FIG. 4,which shows that the collar C of the syringe is still at a shortdistance from the portion of the lower body that defines its prickingposition. At this moment, the leading surface of the second radialprojection 53 causes the pivot members 7 to pivot still further bypushing on their second projections 72. This tensions or loads theresilient elements 8 still further, which elements thus oppose anincreasing force against pivoting of the pivot members 7. This “braking”or “damping” force is represented by arrow F1 in FIG. 12. This generatesdamping at the end of pricking, by decreasing the force exerted by thepiston rod 5 on the syringe S, thereby greatly improving the comfort ofthe user and avoiding damaging the collar C of the syringe S. This canbe seen in FIGS. 5 to 7. Naturally, the forces of the actuator spring 6and of the resilient elements 8 are selected so that pricking is onlydamped without being stopped.

As the pivot members 7 pivot during the pricking stage, the resilientelements 8 become increasingly tensioned. Simultaneously, the movablepins 78 of the pivot members 7 move progressively towards the stationarypins 79. The device is advantageously adjusted so as to generate maximumtorque at (or just prior to) the end of the pricking stage. The neutralpoint in which the movable and stationary pins are in alignment may thusbe reached at (or just prior to) the end of the pricking stage.

When the pivot members 7 and the resilient elements 8 are in the neutralposition, shown in FIG. 8, the piston rod is still urged axially by theactuator spring 6. Thus, the neutral position is not stable, and thesystem toggles automatically from the state of braking pricking to thestate of amplifying the beginning of injection. Optionally, the thirdprojection 73 may be arranged relative to the second projection 72 sothat, immediately after passing the neutral position, the pivot members7 pivot a little under the effect of the tensioned resilient elements 8.This may enable an audible sound to be generated when said thirdprojection 73 hits the second radial projection 53 of the piston rod, soas to inform the user of the beginning of the injection stage.

When the needle A reaches its pricking position with the needle fullyinserted, the injection stage is triggered, and this is shown in FIGS. 9to 11. The leading end 55 of the piston rod then pushes on the piston Punder the effect of the force exerted by the actuator spring 6. Duringthe entire injection stage, the piston rod 5 slides inside the syringeS, pushing the piston P of said syringe under the effect of the spring6. The fluid is thus dispensed through the needle A.

At the beginning of the injection stage, the third projection 73 of eachpivot member 7 thus comes into contact with the trailing surface of thesecond radial projection 53. As at the end of the pricking stage, thetorque exerted by the system is at a maximum immediately after theneutral position, and the tensioned resilient elements 8 thus urge thepivot members 7 strongly in pivoting. This causes the force of theactuator spring 6 to be amplified at the beginning of the injectionstage. This amplification force is represented by arrow F2 in FIG. 13.This amplification increases the force exerted by the piston rod 5 onthe piston P, and thus makes it possible to guarantee that the piston Pstarts to move from its rest position, without having to increase theforce of the actuator spring 6. Specifically, the maximum resistanceduring the injection stage is created when starting movement of thepiston P. Once injection has begun, the friction of the piston P in thesyringe S, the viscosity of the fluid to be injected, and the resistanceof the narrow passage of the needle A are smaller and thus no longerrequire the same force from the actuator spring 6.

As can be seen in FIG. 11, the pivot members 7 are disengaged from thepiston rod after an injection stroke of the piston rod 5 that isrelatively small, typically a few millimeters, e.g. about 4 millimeters(mm) in the embodiment shown. From this disengagement, the systembecomes inactive, and the injection of the fluid follows in the usualway. Optionally, provision could be made for the pivot members 7 tocontinue to pivot after disengagement, e.g. so as to generate a soundthat is audible to the user. It may also be envisaged to adapt theforce-adjustment system so that it can amplify the force exerted on thepiston P for a greater fraction of the injection stroke, e.g. about 20mm, or for the entire injection stroke, in particular with reservoirshaving an axial dimension that is short.

With reference to FIG. 17, the various components of the autoinjector,in an advantageous second embodiment, are shown in exploded view.

This second embodiment is similar to the above-described firstembodiment, and only the differences relative to the first embodimentare described in greater detail below, general operation being similar,if not identical, between the two embodiments. The elements that aresimilar or identical thus have the same numerical references in bothembodiments.

As can be seen in FIG. 17, this second embodiment differs from the firstembodiment mainly by the presence, in the lower body, of an actuatorsleeve 100 that is suitable for sliding relative to said lower body 1between an initial rest position, prior to actuation, in which itprojects axially out from said lower body 1, an actuated position inwhich it is moved axially towards the inside of said lower body 1, and afinal safety position in which it once again projects out from saidlower body so as to cover the needle of the syringe S after injection.It should be observed that the final safety position may be identical tothe initial rest position, or, in a variant, the two positions may bedifferent, e.g. with the actuator sleeve axially extending out from saidlower body 1 in said final safety position further than in said initialrest position. The actuator sleeve 100 is advantageously urged axiallytowards the outside of said lower body 1 by a spring 110 so that, priorto actuation, the actuator sleeve 100 is urged towards its initial restposition and, after actuation, the actuator sleeve 100 is urged towardsits final safety position.

The lower body 1 may also contain an inner body 120 that receives areservoir support element 130 into which the syringe S is inserted.

In this second embodiment, the pivot members 7 are advantageouslyassembled in pivotable manner on the sleeve 3. In a variant, they couldbe assembled in some other way, in particular on the lower body 1 or onthe upper body 2.

FIGS. 18 to 20 show the particular arrangement of this secondembodiment, and in particular the arrangement of the pivot members 7 andof the resilient elements 8 that are likewise springs in thisembodiment.

The operating sequence is shown firstly in FIGS. 21 to 25, which arevertical section views with the springs omitted, and in FIGS. 26 to 30which show the states of the spring 8 in the various positions of FIGS.21 to 25.

Thus, FIGS. 21 and 26 show the rest or storage position prior toactuation. In FIGS. 22 and 27, the pricking stage is taking place, andthe pivoting of the pivot members 7 causes tension to increase in thesprings 8, thereby generating the above-described braking effect. InFIGS. 23 and 28, the pivot members are at the neutral point, with thesprings 8 tensioned as much as possible. In FIGS. 24 and 29, theinjection stage has begun with the above-described amplification effect,as generated by the springs 8 relaxing. Finally, FIGS. 25 and 30 showthe pivot members 7 in their disengaged position with the springs 8relaxed.

Typically, it is possible to obtain damping and/or amplification forcesF1, F2 of about 30 newtons (N). Naturally, other damping and brakingvalues could be obtained by selecting in appropriate manner theresilient elements 8, and by dimensioning in appropriate manner thepivot members 7.

It should be observed that the braking force F1 at the end of prickingis not essential, and that the present invention may provide only theamplification force F2 at the beginning of injection. In thisconfiguration, the pivot members 7 and the resilient elements 8 arearranged so that they only exert said amplification effect at thebeginning of the injection stage. Applying a braking force Fl at the endof pricking is thus optional.

FIGS. 31 to 34 show another embodiment of the autoinjector in whichthere is no automatic pricking, or auto-pricking. It should be observedthat these figures are diagrammatic only and non-limiting of such anembodiment. In this embodiment, the actuator spring 6 performs injectiononly, by moving the piston rod 5, and thus the piston P, between therest position and the injection position. In this embodiment, prickingis performed manually by means of the actuator sleeve 100. In thisembodiment, the syringe S is thus stationary relative to the body of theautoinjector.

In the rest position shown in FIG. 31, the actuator sleeve 100, urged byits spring 110, surrounds the needle A of the syringe S. When the userwishes to actuate the autoinjector, the user places the axial endsurface 105 of the actuator sleeve 100 against the injection site andpresses on the autoinjector. The actuator sleeve 100 then slides axiallytowards the inside of the lower body 1, thus exposing the needle A ofthe syringe S that then penetrates into the body of the user, as can beseen in FIG. 32. The user may then actuate the axial button 4 so as tomove the piston rod 5, and the force-adjustment system then becomesactive as described above, acting via the pivot members 7 to exert anamplification force F2 on the piston rod 5 at the beginning ofinjection, as shown in FIG. 33. FIG. 34 shows the pivot members 7disengaged from the piston rod 5, the end of injection thus continuingwithout any action from said pivot members. In a variant, it could beenvisaged to cause the pivot members to act during the entire injectionstage. In the embodiment shown, in the rest position, the pivot membersare prevented from pivoting by a locking system 200 that isadvantageously released by an axial extension 101 of the actuator sleeve100 at the end of pricking, as shown diagrammatically in FIGS. 31 and32. Naturally, such a locking system is not essential, and it could bemade in some other way.

In this embodiment, the force-adjustment system thus exerts only theamplification force F2 at the beginning of injection, and does notintervene during pricking.

The present invention applies to devices used in particular fortreatment of auto-immune diseases, e.g. of the rheumatoid arthritis,multiple scleroses, Crohn's disease type, for treatment of cancer, forantiviral treatments, e.g. of the hepatitis type, for treatment ofdiabetes, for treatment of anemia, or for treatment of allergy attacks,e.g. in the event of anaphylactic shock.

Although the present invention is described above with reference toseveral advantageous embodiments, naturally various modifications arepossible for the person skilled in the art, without going beyond theambit of the present invention, as defined by the accompanying claims.

1. An autoinjector comprising a body (1, 2), and a reservoir (S)containing fluid and including a piston (P) and a needle (A), such as apre-filled syringe, said autoinjector further comprising a piston rod(5) that is suitable for co-operating with the piston (P) of saidreservoir (S), said piston rod (5) being movable between a rest positionand an injection position in which said piston rod (5) has moved thepiston (P) of the reservoir (S) so as to inject the fluid through theneedle (A), an actuator spring (6) being provided so as to urge saidpiston rod (5) towards its injection position, the autoinjector beingcharacterized in that it further comprises a force-adjustment system (7,8) that exerts a force (F2) on said piston rod (5), said force (F2)adding to the force exerted by said actuator spring (6) on said pistonrod (5) at the beginning of injection, so as to amplify the forceexerted on said piston (P) by said piston rod (5) at the beginning ofinjection, said force-adjustment system (7, 8) comprising two pivotmembers (7) that co-operate with said piston rod (5), said pivot members(7) being connected together by two resilient elements (8).
 2. Anautoinjector according to claim 1, wherein said pivot members (7) pivotabout pivot pins (79) that are parallel and stationary relative to saidbody (1, 2).
 3. An autoinjector according to claim 1, wherein saidresilient elements (8) are fastened to said pivot members (7) viaparallel movable pins (78), such as rods having two side edges, that areformed on said pivot members (7).
 4. An autoinjector according to claim2, wherein, when the piston rod (5) moves towards its injectionposition, said movable pins (78) are arranged behind said stationarypins (79) in the travel direction of said piston rod (5), said loadedresilient elements (8), at the beginning of travel of the piston rod (5)towards its injection position, causing said pivot members (7) to pivotin such a manner as to relax said resilient elements (8), therebycreating an amplification force (F2) at the beginning of injection. 5.An autoinjector according to claim 1, wherein each pivot member (7)includes a plurality of projections (71, 72, 73) that are suitable forco-operating with a plurality of radial projections (52, 53) of thepiston rod (5).
 6. An autoinjector according to claim 1, wherein saidautoinjector is triggered by an axial button (4), one or more sidebuttons (40), or a slidable sleeve (400).
 7. An autoinjector accordingto claim 1, wherein, prior to injection, said piston rod (5) isinitially moved by said actuator spring (6) between said rest positionand a pricking position in which said piston rod (5) has moved saidreservoir (S) relative to said body (1, 2) so as to perform pricking. 8.An autoinjector according to claim 7, wherein, during pricking, thepiston rod (5) co-operates with the piston (P) of the reservoir (S) soas to move said reservoir (S) relative to the body (1, 2).
 9. Anautoinjector according to claim 7, wherein, during pricking, the pistonrod (5) includes a resilient member (9), such as an O-ring arranged in agroove of the piston rod, that co-operates with a collar (C) of thereservoir (S) so as to move said reservoir (S) relative to the body (1,2).
 10. An autoinjector according to claim 7, wherein, when the pistonrod (5) moves from its rest position towards its pricking position, saidmovable pins (78) are arranged in front of said stationary pins (79) inthe travel direction of said piston rod (5), said piston rod (5), at theend of travel towards its pricking position, causing said pivot members(7) to pivot so as to load said resilient elements (8), thereby creatinga braking force (F1) at the end of pricking.
 11. (canceled)